poisonous
- 1Containing enough poison to be dangerous to touch or swallow.
Many household cleaners are poisonous if swallowed.
The plant's leaves are poisonous and can irritate the skin on contact.
Similartoxic, venomous, poisoned
Oppositenontoxic, harmless, edible
Note
The core sense is built plainly from poison and -ous, carried over from Middle English poisounous. It covers what harms you when touched or swallowed: a mushroom, spearwort's leaf, a household cleaner. The danger is often relative, highly poisonous to dogs yet harmless to people. Careful writers keep venomous for creatures that inject their toxin, the job that the snake-and-spider meaning does more loosely.
- 2Of an animal or its bite or sting: producing a toxin that is injected into prey or an attacker by biting or stinging.
The region is home to several poisonous snakes whose bites require immediate treatment.
A poisonous sting from the scorpion left her arm swollen for days.
Similarvenomous
Oppositenonvenomous, harmless
Note
Naturalists long used the word this way, and it is the use that careful writers resist. John Wilkins in 1668 sorts serpents by whether they are poisonous, and Leonhard Stejneger titled his 1895 study The Poisonous Snakes of North America. The use remains common in everyday speech, but venomous is the more precise choice for snakes, spiders, bites and stings. Poisonous then stays with what harms on touch or swallowing.
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Practice
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Origin
From Middle English poisounous (also poysonouse). By surface analysis, it is poison plus the suffix -ous.